Processing of lightweight aggregates



Aug. 17, 1937. c. F'. MEINZER` PROCESSING OF .LIGHTWEIGHT AGGREGATES.1.o .W21 W r fr! J'T/yeuger,

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Patented Aug, 11, 1.937

UNITED STATES PROCESSING oF LIGHTWETGHT AGGREGATES Carl F. Melnzer,Chicago, Ill., asslgnor to Wallace L. Caldwell, Birmingham, Ala.

Application February s, i935, serial Nofsssv fc claims. (ci. :i3-e4)This invention relates to light Weight aggregates having improvedphysical properties for use in concrete anda process for improving saidphysical properties. Y

Light weight aggregates are,` ucts of four different classes:

in general, prod- (1) Synthetic cellular or porous products pro-- ducedfrom molten metallurgical slag by processes of granulation or agitationwhich cause the slag to expand and develop a cellular structure beforecooling.

(2) Synthetic cellular products produced from burned clay, shale orother ceramic'materials by processes which cause the material to expandand develop a cellular structure, veither before thev glass Whilemolten, with solidiiication to a cellular porous structure.

(4) Natural cellular products produced by the crushing of natural porousrocks such as pumice, tu or tufa.

All oi. these light weight aggregates are produced by their variousprocesses of manufacture, in some cases with and in other cases Withoutsupplementary crushing. in sizes such as are customarily required foruse in ccncretes using Portland cement or other hydraulic camente.

These light weight cellular aggregates are commonly characterized by e1y rough and angular surfaces with numerous jagged projections andcavities. These products are also characterized by numerous checks orplanes of cleavage in the internalstructure of the particles ofaggregate. These cleavage planes, for the most part, develop as a resultof stress set up within the material while cooling from a moltencondition. lt is to be understood, however, that my invention is notlimited to the above class of material since the broad concept thereofcontemplates improvement ci any type aggregate wherein the same problemis presented.

The rough, angular surfaces, with projections and cavities, causeconcrete e from such aggregates to be harsh and unworlsable. Fmthen-.more aggregatecomposed oi individual pieces having the characteristicsdescribed, has a materially higher percentage ci voids than aggregateshaving the mrticles somewhat more ro 1 :wf ed and free from rough,jagged edges and projections. The rterm voids is dejned as the spacesurrounding and between the individual particles of aggregate and shouldnot be conf with the cells or pores in the individual pieces ofaggregate.

This invention has as one of its objects the reduction in the percentageof voids in light weight aggregate. One of the essential properties ci?any concrete is that it have sufiicient plasticity to ilow into place ina form or mold or slab without an excessive amount of tamping. Concretesmade from unprocessed light Weight aggregates, having the propertiesherein described, are decidedly unwofrkable with the resuit that it isdiiiicult to use them. in actual construction practice without excessivelabor cost,

and without the necessity of increasing the cement content of theconcrete to an unreasonably high ligure. A high cement content and ahigh percentage of water will, to some extent,

`4aidin the Workability of a concrete mixture, but

the cost of such extra cement is high and the use of an excessively highwater ratio causes undue shrinkage and segregation in the concrete. Itis one of the purposes of this invention to improve these light Weightaggregates with respect to their Workability, strength and economy whenused in various types of concrete mixtures.

Another inferior characteristic of such light weight aggregates is thepresence of numerous cleavage planes in the particles of aggregates asordinarily produced. These cleavage planes are a distinct source ofweakness in such aggregates. These cleavage planes produce areas of lowstrength in the concrete produced with such aggregates, and therebycause such concretes to have lower tensile and compressive strengthsthan is the case when such cleavage planes are eliminated. These planesalso give entrance to moisture when the particles of aggregate are onthe exposed surfaces oi concrete. Such in'- ternal moisture causesconcrete to disintegrate if exposed to freezing and thawing. It is oneof the purposes of this inventionv to improve light weight aggregates byeliminating a jorlty of these cleavage planes in particles of theaggregate, thereby improving their quality with reobjectiveaccomplis-hed through this invention is the removal of the more denseand heavier surface skin of the particles., thereby producing an.

I larly the planes of cleavage or planes of incipient fracturecharacteristic thereof.

Fig. 3 is a side elevational view of aggregates formed from theaggregate shown in Fig. 1 after processingfparticularly illustrating theabsence of surface projections and crevices.

Fig.v 4 is a sectional View of the processed aggregate shown in Fig. 3,illustrating particularly the absence of planes of cleavage or planes ofincipient fracture. v

' Fig. 5 is a sectional view of a piece of concrete comprising.unprocessed light-weight aggregate, showing particularly the presence ofvoids adja cent the projections andcrevices of the aggregates.

3@ Fig. 6 is a similar view of the same piece of concrete afterweatheringrshowing failures due to the presence of planes of cleavage inthe aggregates.

Fig. 7 is a sectional view of a piece of concrete comprising theprocessed aggregate of my invention.

Referring in detail to the drawing, I indicates a piece of unprocessedlight-weight'aggregate of the type hereinbefore described, characterizedby having a jagged external surface. Complementary to the jaggedprojections are a plurality of crevices 2 which together with saidprojections create an abnormal number of voids when the aggregate isused in concrete. By referring to Fig. 2, it will be seen that theaggregatel contains many planes of cleavage' or planes of incipientfracture 3 which seriously weaken the aggregate.

In carrying out the present invention, light weight cellular aggregate,with rough, irregularv and angular surfaces and projections, such asaggregate I, is charged in a container (not shown) which is rolled orrotated .for a limited period oi. time. During this treatment thesurfaces and edges of the pieces'of the light weight aggregate areslightly rounded, and the characteristic rough and jagged projectionsare either wholly or partially removed as shown best at 4 in Fig. 3. Therolling of the particles or pieces of light weight aggregate overoneanother produces a mild grinding action without crushing or breakingthe particles except upon cleavage planes or lines oi weakness producedby internal stresses developed during cooling. 'I'his breakage oncleavage planes results in the larger particles of the materialcontaining such cleavage planes being converted'into smaller particlesfree from checks or cracks caused by cleavage planes. The process canbest be accomplished in a hollow,

v rotating, steel or metal cylinder having small perforations in theshell for the purpose of removing the fine material which accumulates asthe result of the grinding action. The process can be accel- 'erated bythe use of ridges, bales or projections 'I5 on the interior o1' thecylinder'and also by the use of a limited number of 11g-ht weight metalor rubber balls. Y

As an example of the manner in which the aggregate in its unprocessedstate is broken to form sound pieces of aggregate, reference isparticularly made to Figs. 2 and 4 of the drawing. As has beenhereinbefore described the unprocessed aggregate I contains a pluralityof planes of cleavage or planes of incipient fracture 3. In theprocessing hereinbefore described the aggregate I in addition to havingsubstantially all of the projections removed, may also crack along theplanes 3 and form a plurality of smaller' pieces of sound aggregate. Forexample, aggregate I maycrack along planes 5 and 6 which may define,when completely broken a small piece 'of Yaggregate I which, as theprocessing continues forms the piece I', a sound, rounded piece ofaggregate. The planes 8 and 9 may meet during the jostling or tumblingof the aggregate to dene the piecek of aggregate I0 which maysubsequently be formed into the sound, rounded piece of aggregate I0. Inthis manner a large piece of unprocessed aggregate may during processingbev formed into. a plurality of sound, relatively smooth surfacedsmaller pieces of aggregate.

Light weight aggregate manufactured under the method covered by U. S.Patent No. 1,483,241, granted to Emil Opderbeck under date oi' February12, 1924, has been thoroughly tested by this process. Specific examplesof' tests showing the improvement in the processed |aggregate over-theunprocessed aggregate follow;

(A) lVcRKBIuTY Tirsrs Determined by Standard Slump Test of AmericanSociety for Testing Materials Concrete mixtures parts by .e

\ 01u11 slump test in inches Light s Using lmproc- Using proo- PortlandSand weight assed aggre. assed sgmcement aggregate l gute gatel'processed aggregate concrete. In actual practice this property is ofthe greatest importance. 'I'his decided change in physical property isbrought about by the removal, during processing, of the rough, angularedges and the jagged surface projections of the pieces of aggregate withconsequent reduction of voids in'the aggregate.

(B) Dnnsrry Tns'rs Unprooessed Pmcessod BSKPBKBO Usmate 0n 0n )4" On 9i"0n M" screen screen screen lenen wt. per cu. u... 4s. 6 4o. o 4L e 42. oSpec. gravity ofaggregate. l. 5 8 1. 39 1. 46 l. 26

The above resultsshow that the processing in- Y '2,090,455 creasesthe-weight per cubic foot oi' the crushed I i 15 is decreased.For-example:

Void: in processed aggregate= 1 46X 62.5

'nie processing of the aggregate reduced the voids from 56% to 51%,while in' the t" aggregate the processing reduced. the voids from y 54%to 47%. This reduction of voids is of great importance technically andcommercially in that it permits concrete mixtures oi suitable strengthto be produced with materially lower cement factors.

The reduction of specific gravity of the indi- 29 vidual particles ofaggregate is of importance in that it holds down the weight of thefinished concrete to within permiible limits.'

These comparative tests can be readily visualized by referring to Figs.5 and '7. In Fig. 5 it will 2" be seen that voids li will be formed in aconcrete block or section l2 by the adjacent disposition of irregularprojections and crevices characteristic of this type of aggregate. Itcan readily be n seen that it would be extremely difficult to cause "0the cement bonding medium, unless excessively liquid, to ll said voids.However, by'using the processed aggregates 4 no difficulty in thisregard is encountered since the surfaces of the aggregate n, are smoothand rounded and offer no resistance to the W of the cement.Consequently, substantially no voids are existent in the finishedconcrete.

4o Measured bgmmersioa in water for one haar,

then drying to constant weightat 105 Assoar'non No Ansoar'rroN TESTSPercentage absorption plus adsorption Processed BBENSMS Unprocessedinsensata The significance of thistest is that the removal of the rough,jagged surface projections reduces the adsorption of surface film ofwater, and also tends to reduce absorption since the surface smn of theparticles before removal is less cellular but has far more capillarypores than the interior of the particles, with result that absorption isgreater in this surface slain.

(D) SoUNDNEss y Tns'rs Determined by American .Society for TestingMatenais Sodium Sulphate Method. This is equivaent to freezing andthawing action of nature, .Resa'ts are expressed n percentage by weightThis test is of great signicance and has been checked a large number oftimes, both by the A. S. T. M. accelerated soundness testandby'actualfreezing and thawing tests both of agi'esate rmd.

of concrete produced. The cleavage planes char-l to water and theaggregate and concrete soon show the eect by very noticeabledisintegration.`

Referring particularly to Figs. 5 and 6, the result of subjecting apiece of concrete containing unprocessed aggregate such as shown in Fig.5 to freezing, or subjecting lthe same to the sodium sulphate test', isshown in Fig. 6. As has been hereinbeforepointedout the unprocessedaggregates I contain a plurality of cracks, planes of cleavage or planesof incipient fracture. If, in pouring the concrete, pieces of .aggregateare disposed adjacent the forms and said cracks are brought intocommunication with the atmosphere, whichsituation is frequently thecase, moisture or water finds its way through said cracks or planesvofcleavage into the interior of the aggregates. If this concrete isthenexposed to freezing temperature, the moisture or Water within saidlcracks expands and tends to rupture the aggregate. This action iscumulative-since each time expansion occurs the crack becomes wider anda greater amount of moisture can penetrate into the aggregate andeventually portions of said aggregate break away from theconcrete'structure as shown best at I3, li and it in Fig. 6. Inaddition, due to the irregular ,surface contour of the unprocessedaggregates i, the outer surface oi the concrete block i2 will be more orless pook mark-ed or honeycombed due to the fact that the cement isunable to settle or rind its'way into the various orevices formed in theface of the aggregate.

In the examples illustrated in Figs. y5 and 6, it will be observed thatvoids li are formed adjacent the outer surface of the aggregate and thatcracks it, il communicate with said voids. Moreover, as shown at iii andis in Fig. 5, cracks open to the external surface of the concrete-blocir i2, consequently, when said block is enposed to moisture orwater, said moisture and water nd its Way into the planes of cleavagesit, il, i@ and i@ and if freezing occurs, said Water expands wideningthe cracks. As has 'been hereinbefore described, said action iscumulative and after repeated freezing and thawing occurs, portions ofthe aggregate disintegrate. For instance, in Fig. 5 the planes ofcleavages i@ and ld may eventually join in which case a piece of theconcrete block breaks away as shown at i@ in Fig. 6. As iilustrated inFig. '7 the` external surface of the concrete block does not contain anyerevices or peck mark since, the aggregate being rounded and smooth, thecement has no difdculty in completely surrounding the aggregate andfinding its way into the'interstices between adjacent pieces ofaggregate. Moreover, in View of the fact that the processed aggregate issound, even if Iportions of the aggregate are in communication with theatmosphere, no cracks or planes of cleavage permit Water to enter .theinterior of the aggregate.

e A' 10 acteristic of unprocessedaggregate give access (E) CoMrREssrvESTRENGTH'TES'TS.

` Concrete-Weight per Compressive strength cu. it. Pounds per sq. in.Cement fac- 4 5 tor-Bags per Cu'yd' Unprocessed Processed UnprocessedProcessed aggregate aggregate aggregate aggregate 4.1 so a7. ses 1,7953.0 sc 77 615 1,100

A large number of compression tests using identical concrete mixtures,except for the aggregate, show that invariably, and for high strengthstructural concrete as well as for low `strength fill concrete, theconcrete mixtures produced with processed light weight aggregates showmaterially higher strengths than concrete using unprocessed aggregate.,

2O I have also found that when I use the processed light weightaggregate in any concrete mixtures, I can materially reduce the `amountof hydraulic cement Which is required lwhen the same light weightaggregate is utilized in its unprocessed form with itscharacteristic-irregular and jagged, surface. By extensive testsI havefound it necessary to use as much as seven (7) bags of hydraulic cementper cubic yard of. structural concrete mixture when utilizing rough,jagged, unprocessed light weight aggregatewhereas I have been able to`reduce the amount of hydraulic cement to five (5) bags or less per cubicyard of concrete when making use of the same light weight -aggregateafter being processed according tc the present invention. The strengthof the concrete produced with the processed light weight aggregate, withtwo v(2) bags of cementless per cubic yard, has

in all instances been-equal orv better than the strength of the mixtureusing the high quantity of cement and the unprocessed aggregate.

Light weight aggregates produced by several different processes, and ofa number of different materials, have been available on the market forseveral years. The advantages resulting from 45 their use in various.types of construction are well known. However, because of the fact thatlight weight aggregates, Vwith their characteristic rough, angular andjaggedsurfaces, do not lend themselves readily to normal flow andworkability 5o in concrete mixtures their use has been greatlyrestricted. Many attempts have been made by concrete workers to overcomethis harshness and' lack of workability, but in practically allinstances the attempted solution was by the use of increased cement andwater ratios which greatly increased the cost, and when excessive waterratios were used, they materially decreased the strength.

It has also been found that whilevunprocessed light weight aggregateproduces concrete with an excess of porosity or honeycomb against forms,

the processed aggregate produces a concrete having practically noporosity or honeycomb against accuses forms, at the same time requiringmuch less cement and less labor.

I claim as my invention: l l. -A method of treating a mass of particlesof light-weight cellular aggregate having a plurality of planes ofincipient fracture which comprises,

subjecting said aggregate to forces o f impact of sufficient intensityonly to rupture said aggregate along said planes of incipient fracture,and without cracking of sound aggregate. i'

2. A method of treating light-weight cellular aggregate having a roughexterior surface and planes of incipient fracture which-extend into theinterior of the aggregate which comprises, subjecting said aggregate toforces of impact of just 'sufficient intensity to rupture said aggregatealong said planes of incipient fracture and simull taneously subjectingsaid aggregate to abrasion to smooth the surfaces thereof.

3. A method of treating light-weight cellular aggregates whichcomprises, agitating a bulk of said aggregates to cause said'aggregatesto abrade and impact one another, just sufficient to smooth the surfacesof said aggregates and cause the aggregates to fracture alongsubstantially all' planes of incipient fracture.

4. A method of treating light-weight cellular aggregates having rough.,irregular exterior surfaces andl planes ,ofincipient fracture whichextendinto'the interior of the aggregates comprising, mildly agitatinga. bulkof said aggregates with just sufficient intensity to cause saidaggregates to abrade and smooth one another's external surfaces, andimpact upon one another to rupture the aggregates substantially onlyalong said planes of incipient fracture.

5. A process for pretreating or polishing light weight cellularaggregate to adapt it for use in concrete mixtures, which comprisescharging a bulk supply of said light weight aggregate to a. container inthe form of particles, rotating said container to cause the particles oflight weight aggregate to roll over one another just suilicient toproduce a mild grinding or polishing action which rounds the edges andsmoothes the surfaces of said particles without cracking sound particlesof aggregate, sifting out of the container the finer aggregatesresulting from the rolling action and recovering the particles formingthe residue of the bulk supply.

6. A process for pretreating or polishing light weight cellularaggregate having planes of incipient fracture to prepare the aggregatefor use in concrete mixtures, which consists in rolling or rotating a-mass of particles of the aggregate whereby the particles of aggregateare caused to roll over and impact one another just sufficient torupture said particles along said planes of incipient fracture andproduce a mild grinding 0r polishing action and rounding the edges andsur- CARL F. MEINZER.

